1. Field of the Invention
The present invention relates to utilizing winter cold more particularly to transmitting and storing winter cold underground for effective uses during summer seasons.
2. Description of the Prior Art
Prior art ground cold storage systems are generally accomplished by blowing winter cold ambient air to pass through the cold reservoir formed by crushed stones and rock beds. In other cases, cold liquid medium is pumped through pipes embedded in stone and rock medium in the form of which constitutes a closed heat-exchange system.
The stones and rocks, as a cold storage reservoir, have several shortcomings. First, cold storage capacities are limited because of the narrow temperature range for cooling. In other words, the difference of storage temperature in winter and upperlimit useful temperatures in summer is less than thirty degrees Fahrenheit (30.degree. F. to 60.degree. F.). For example, in a volume of one cubic foot of stone at a temperature difference of 30.degree. F., the energy flux is about 1.3.times.10.sup.3 BTU. Assuming a summer requirement of 25.times.10.sup.6 BTU for an average size home, a volume of cold storage required for cooling is estimated at 20.times.10.sup.3 cubic feet. In contrast to this large volume, if ice is used for cold storage instead of rock, the required storage volume is about 2.5.times.10.sup.3 cubic feet.
Another shortcoming of the stone and rocks as cold storage is the low thermal conductivity. It would require a long length of liquid pipes and considerable pumping power in order to meet the maximum cooling rate required during hot summer days.